The present invention relates to a new and unique variation of, and improvement over, conventional inverted roof structures. As a result of the practice of this invention, an inverted roof structure can be constructed which possesses superior fire-retardant, protective, and insulative properties, while concurrently significantly reducing the overall weight of the composite roof structure. It is an important feature of this invention that such improved structure can be constructed independent of the pitch angle the roof structure forms with the horizontal.
The method and structure of inverted roof systems is well known and practiced by members of the building profession. For example, U.S. Pat. No. 3,411,256, held by the Dow Chemical Company, (hereinafter, "Dow"), discloses an inverted roof structure, and method thereof, which comprises a roof deck, water impermeable membrane, closed cell water impermeable thermal insulating member, and a water permeable protective layer. This structure reduces exposure of the water impermeable membrane to adverse environmental conditions, thereby protecting the membrane and extending the useful like of the roof structure.
While the structure taught by Dow is now used throughout the building industry, the structure possesses several signficant limitations which renders it generally unsuitable for use under many naturally existing conditions. For example, inasmuch as the protective layer is water permeable, moisture passing therethrough ultimately contacts the underlying water impermeable membrane and can cause cracking of said membrane due to cyclical freezing and thawing conditions. Further Dow recognizes that the thermal insulation member is subject to decomposition, particularly when exposed to sunlight; however it fails to disclose a method by which the insulating member may be permanently protected from such elements. Still further, a roof structure constructed in accordance with the Dow disclosure utilizing styrene for the thermal insulation member requires approximately 1200 pounds of gravel per 100 square feet of roof surface area in order to receive an Underwriter's Laboratories Class A rating for fire retardancy. Finally, Dow fails to disclose a method by which the protective layer can be applied regardless of pitch angle, and, by necessity, structures constructed in accordance with the method of the invention are limited to low pitch angles.
Therefore, it is an object of the present invention to provide a roof structure which substantially inhibits the absorption of water which may adversely affect the water impermeable membrane.
Yet another object is to provide a protective layer which effectively inhibits deterioration of the underlying thermal insulation layer due to foot trafic and adverse environmental conditions.
A still further object is to provide a roof structure which may be constructed without roof pitch angle limitations.
And yet another object is to provide a roof structure characterized by superior insulative and fire retardant qualities while simultaneously achieving an overall reduction in the weight of the structure.